What is this tube?

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What is this tube?

Post by Patrick on Mon Jan 27, 2014 5:34 pm

I started to restore an old Imperial radio model 579-1-58A. There is no tube location diagram on the case or chassis. I cannot find a schematic either. The radio works fairly good as it is but I want to re-cap it, clean it up and check the tubes. It has 2-12SK7s, 12SA7, 12SQ7, 50L6 and a tube I cannot find the number. It must be the rectifier and probably a 35Z5 but the puzzling thing is the tube has a tiny wire soldered from the number 2 to the number 3 pin. Can anyone tell me the number of the tube and the reason someone connected the two pins.
Thanks

Patrick
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Re: What is this tube?

Post by Wildcat445 on Mon Jan 27, 2014 6:08 pm

Yep.  That kluge was commonly done when the dial bulb burned out, and the tap in the filament of the rectifier opened.  The rectifier would not work then.  The jumper was put there to bridge the open and would allow the rectifier to work.  I would strongly recommend replacing the filter capacitors, checking B+ for a short, replacing both the rectifier and the dial bulb, if any.  If there is no dial bulb, there should be a small resistor across that tap to replace the dial bulb.  The service literature for your set should provide the number for the dial bulb and also the value of the resistor if the bulb is not used.  You should also check the wiring and socket for the dial bulb to be sure there is not a problem there.  I would not operate this radio with the jumper installed.  Fix it properly to prevent problems down the road and for the radio to be safe to use. The rectifier is most likely a 35Z5.

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WC

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Re: What is this tube?

Post by kent3256 on Sat Feb 22, 2014 11:08 pm

One thought....the filament voltages listed total 98V, actually a little more...so it might be a 25Z5, rather than a 35V tube....would make the filament total come out pretty close to 120.
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Re: What is this tube?

Post by Patrick on Sat Feb 22, 2014 11:17 pm

Makes sense. Thanks for pointing this out.

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Re: What is this tube?

Post by Bill Cahill on Sun Feb 23, 2014 9:21 pm

25Z5 would not be an octal tube. A 25Z6 would be octal, but, a two section tube.

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Re: What is this tube?

Post by Wildcat445 on Sun Feb 23, 2014 9:36 pm

I would put the 35Z5 back in and not worry about the lower voltage.

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WC

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Re: What is this tube?

Post by Dr. Radio on Sun Feb 23, 2014 9:46 pm

As indicated in the original post: 2-12SK7s, 12SA7, 12SQ7, 50L6 and a tube I cannot find the number. It must be the rectifier and probably a 35Z5.



Typically you have (2) 35 volt tubes in 6-tube line-ups.


12+12+12+12+35+35 = 118

Radio most likely came with a 35Z5 rectifier and 35L6 output tube.
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Re: What is this tube?

Post by Guest on Sun Feb 23, 2014 9:51 pm

Dr. Radio wrote:As indicated in the original post: 2-12SK7s, 12SA7, 12SQ7, 50L6 and a tube I cannot find the number. It must be the rectifier and probably a 35Z5.



Typically you have (2) 35 volt tubes in 6-tube line-ups.


12+12+12+12+35+35 = 118

Radio most likely came with a 35Z5 rectifier and 35L6 output tube.


Now this makes the most sense!  Wink 

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Re: What is this tube?

Post by Bill Cahill on Mon Feb 24, 2014 10:20 am

Yes, but, I leave a 50L6 in because the original line up was originally for 115 volt. I find that leaving in the higher voltage tube does fine. Radio will still play great, and, it's less stress on filament line.
If you have the dial light with that set yet, don't forget to remove that shorting wire, and, of course, make sure the six volt tap on your replacement tube isn't burned out.

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